1. Field of the Invention
The present invention relates, in general terms, to clutches, that is to say mechanical devices to be put to use between two coaxial parts mounted so as to rotate relative to one another, in order, as required, to make either a connection between these two parts in terms of rotation or a break between them.
It is concerned more particularly, but not necessarily exclusively with the equipping of motor vehicles.
2. Description of the Related Art
In such a case, there can be either an actual clutch, that is to say the device to be interposed between the output shaft of the engine and the axle shafts when the corresponding transmission is a mechanical transmission, or a simple clutch unit of the type which, when this transmission is a hydraulic transmission, is used within the corresponding hydraulic coupling member, in order, for example, to ensure, under certain transmission conditions, a direct engagement between the shafts in question, deactivating such a hydraulic coupling member, or a direct connection between the housing of the latter and its turbine wheel.
Where an actual clutch for mechanical transmission is concerned, as is known such a clutch comprises substantially a first plate, or reaction plate, which is intended to be fixed in terms of rotation to a first shaft, generally a driving shaft, and in practice the output shaft of the engine in respect of the equipment of a motor vehicle, a clutch plate assembly with a friction disc and hub, intended to be fixed in terms of rotation by means of the said hub to a second shaft, generally a driven shaft, and in practice the input shaft of the gearbox in respect of such equipment, a cover which is fixed in terms of rotation to the reaction plate, a second plate or pressure plate, and axially acting elastic means which, bearing on the cover, are designed to stress the pressure plate in the direction of the reaction plate, in order to clamp the friction disc of the clutch plate assembly and thus engage the unit as a whole.
Within such a clutch, in practice the friction disc of the clutch plate assembly forms the actual clutch unit and torque is transmitted between the driving shaft and the driven shaft as a result of friction by means of this friction disc, and more specifically friction linings which it possesses for this purpose.
Most often, a clutch thus has only a single clutch unit, and because of its construction there is never any slip in the region of the latter, apart from the transient conditions prevailing during engagement or disengagement, and for this purpose the maximum torque which it is capable of transmitting without slip is deliberately selected higher, bearing in mind a reasonable safety coefficient, than the maximum engine torque.
This clutch is likewise usually employed to ensure filtering of the vibrations which may arise over the entire length of the kinematic chain formed by the transmission on which it is placed.
In practice, to achieve this, a torsion-damping device is arranged there.
Most often, this torsion-damping device is incorporated in the clutch plate assembly between its friction disc and its hub.
However, alternatively or in addition, there has already also been a proposal to incorporate such a torsion-damping device in the reaction plate.
At all events, hitherto such a torsion-damping device has conventionally used, between two coaxial parts mounted so as to rotate relative to one another, on the one hand, circumferentially acting elastic means and, on the other hand, for the desired damping, friction means.
This arrangement has been and still is satisfactory, at least for some uses.
However, it has the following disadvantages.
First of all, it virtually unavoidably generates noise.
In particular, there are the noises called neutral noises, that is to say the noises which, with the gearbox in neutral, are attributable to knocking between the pinions of such a gearbox under the stress of the cyclic irregularities of the engine and the angular oscillations resulting from these in the component parts of the torsion-damping device used.
There are also the noises called "clunk" noises, that is to say the noises which occur, for example, when the vehicle driver more or less abruptly releases the depressing action which he previously exerted on the vehicle accelerator, the mode of operation of the unit as a whole then changing from the type called "traction" in which the engine torque outweighs the resistant torque, to the type called "on the overrun" corresponding to operating conditions which are the opposite of the preceding one.
In fact, since the circumferentially acting elastic means contained in the torsion-damping device used are saturated very quickly, each time this results in a virtually instantaneous and therefore noisy tilting of one of the component parts of this damping device in relation to the other, this tilting corresponding to a relative bearing change from one circumferential direction to the other between the said parts, the relative angular movement between these inevitably being limited, each time with compensation of the mechanical play existing downstream in the transmission in question, and especially in the bridge which the latter normally possesses.
This "clunking" noise, which also arises when a new depressing action is exerted on the accelerator, is especially noticeable when the vehicle is driven in a slow-moving line, that is to say when, as can happen, for example, in town traffic, the speed of this vehicle is low, for example near the normal idling speed of the engine, and when, in conjunction with this, the torque required from the latter is also low, engines equipping some vehicles at the present time being designed, in fact, so that they are capable of accepting such operating conditions in order to minimize consumption.
Moreover, it can be accompanied by rocking which, when transmitted to the engine and from this to the body of the vehicle in question, can give rise in this body, especially when the engine is arranged transversely relative to this, to an oscillatory movement, commonly called a "knocking" movement which reflects that to which the two component parts of the torsion-damping device in question are then subjected and which can give the driver of such a vehicle an unpleasant feeling.